Imperative Role of Oxidation of Diethylthiourea in Dye Wastewater Treatment

Several properties of thiourea and its derivatives are reported in biological, electrochemical,
photochemical and radio-protective fields. This article proposed the use of thiourea derivative in the
field of dye wastewater management where the color of the dye was reduced by the application of
Diethylthiourea (DETU). For this purpose basic dye methylene green (MG) was selected at
laboratory scale to monitor its color reduction by the addition of DETU. It was observed that DETU
reacts with methylene green (MG) and reduced it into leuco dye where it oxidized into smaller
fragments like urea, nitrate and sulphate. The reaction was favorable in acidic condition. A direct
relation in between oxidation of DETU and MG to the concentration of H+ ions was observed through
typical kinetics in two acids like HCl and H2SO4. The second order kinetics with respect to HCl and the
first order with respect to H2SO4 indicated the protonation of the dye leading to reduction. In alkaline
medium, the decline in the rate of reaction may be due to the suppressing effects of alkali on
oxidation/degradation of DETU into smaller fragments or may be attributed with the de-protonation of
DETU. Influence of addition of dye into reaction mixture retarded the bleaching process and follows
zero order kinetics while rate of reaction enhanced by the addition of DETU in the reaction mixture
and shows ¾th order with respect to DETU. Negative effect of added different electrolytes reflects that
change of ionic strength of reaction mixture have some bearing on redox reaction of MG and DETU.
Reaction was monitored at elevated temperature and activation parameters were computed. The
mechanisms of oxidation of DETU with reduction of dye MG were discussed. Reduction of MG into
leuco dye with the fragmentation of DETU was observed in acidic condition at elevated temperature.